Name: 1. A heterozygous short haired cat is crossed...

Maribyrnong College Biology Unit 4 - Genetics Problems 2012

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Name: _______________________________

1. A heterozygous short haired cat is crossed with a long haired cat. The expression of the short haired allele is dominant over the expression of the long haired allele. What is the chance (probability) of producing a short haired kitten? Show all working below.

Write a Genetic Hypothesis Define allele symbols: Short = Long = P phenotypes x P genotypes x P Ova/sperm Punnett square

F1 genotypes F1 phenotypes Answer =


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2. In mice, grey coat colour is dominant to black. What is the genetic hypothesis? What symbols could be used to represent the alleles for these coat colours? If a pure-bred grey mouse is bred with a black mouse, set out the genetic cross showing all phenotypes and genotypes in the P and F1 generations. A pet shop owner only wants to sell black mice, because they are worth more money than grey. What phenotypes and genotypes of the parents would guarantee only black mice in the offspring? Explain fully.


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3. Albino (white) coat colour in rabbits is recessive to brown coat colour. What is the genetic hypothesis? What symbols could be used to represent these coat colours? Brown = Albino = What genotypes are possible if a rabbit has a Brown coat = Albino coat = A brown rabbit that had one albino parent was crossed with another brown rabbit which also had one albino parent. What are the expected proportions of genotypes and phenotypes amongst the offspring (F1) resulting from this cross? Show all working out below


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4. Feather colour in Andalusian poultry is determined by incomplete inheritance. The most prized fowls are blue in colour and they are known to be the heterozygous. When blue fowls are allowed to breed with each other, they produce offspring that are either black, blue or whitish. What is the genetic hypothesis? How many phenotypes are there for feather colour in Andalusian poultry? What symbols could be used to represent the alleles for these coat colours? (Hint: there are only TWO alleles) Write down the genotypes for each of the phenotypes. A black fowl is mated with a whitish fowl. Complete the following to show phenotypes and genotypes of their offspring (the F1).


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5. In guinea pigs rough coat is dominant to smooth coat. What is the genetic hypothesis? What symbols could be used to represent the alleles for these coat types? If two heterozygous rough-coated guinea pigs are mated, what types of genotypes and phenotypes would you expect? Show all working. A rough-coated guinea pig is bred to a smooth one, giving 8 rough and 7 smooth offspring in the F1. Show phenotypes and genotypes for the parents and the F1 generation.


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6. In tomatoes red fruit colour is dominant to yellow. Suppose a tomato plant homozygous for red is crossed with one homozygous for yellow. Determine the appearance (phenotype) of the F1, and the F2 To produce the F2, plants from the F1 were allowed to interbreed. Show all working.


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7. Coloured coat in mice is dominant to white coloured mice. If a pure-bred coloured mouse was mated with a pure-bred white mouse, what genotypes and phenotypes would there be in the offspring? Use The Eight Steps and show all working out, including a Punnett square.

If two of the offspring mated, what colour will their children be and what ratio of coloured mice to white mice will result. Use The Eight Steps and show all working out, including a Punnett square.


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8. On a sheep farm in the Mallee for over ten generations most of the sheep bred there have been white. Occasionally though, a white ewe has given birth to a black lamb. Whenever two black sheep breed, only black lambs are born. When pure-breeding white sheep are crossed, they only produce white lambs. However, some white sheep, when crossed, regularly produce both white and black lambs. What is another term for pure-breeding? What are the phenotypes for sheep coat colour? What is the genetic hypothesis? Write symbols to represent the alleles for coat colour. Write down the genotypes for each of the following:

the pure-breeding white sheep

a white sheep that produces black lamb

black sheep Complete the following cross to show a mating between two heterozygous white sheep. Write down the expected proportions of phenotypes in the offspring.


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9. Straight hair is dominant to curly hair in mice. Two different matings were set up I. A homozygous straight haired male with a curly female II. A heterozygous straight haired male with a curly female

Write a genetic hypothesis for each cross. State a symbol for each of the straight haired allele and the curly allele.

What are the genotypes of each of the parents in each of the matings? I _______________________________________ II _______________________________________ Use 2 punnet squares to work out the genotypes and phenotypes of the offspring of each cross I Offspring genotype______________________________ Offspring phenotype_____________________________ II

Offspring genotype______________________________ Offspring phenotype_____________________________


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10. The length of tail in cats is an example of Dominance inheritance and also a lethal genotype. The symbol for long tail is Tm and the symbol for no tail is TM. Cats with genotype TMTM die before they are born. Cats with genotype TMTm are called Manx cats and have a very short, stumpy tail and cats with genotype TmTm have a normal tail length. If two manx cats mate what is the probability (chance) that any kitten will have a normal tail? What will be the proportion of Manx cats (i.e. not tails) born? Use The Eight Steps and show all working, including a Punnett square.


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11. When long radishes are crossed with round radishes, all the offspring are oval. If these oval radishes were then crossed with one another, what would you expect the next crop of radishes to be like?


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12. In tomatoes there is a dwarf form (homozygous recessive) that is determined by a gene on chromosome 1. Also in tomatoes, yellow coloured fruit (homozygous recessive) is due to a gene on chromosome 2. A pure breeding normal height yellow fruit tomato plant is artificially pollinated from a pure breeding dwarf red fruit plant. The progeny are then artificially pollinated with each other. Using The Eight Steps set up the crosses and Punnett Squares for the original cross between the pure breeding parental plants and then repeat the process for the cross between the resulting F1

plants showing all the possible genotypes and the ratio of possible phenotypes in the F2 generation.


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12. continued


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13. Individuals who lack an enzyme needed to form the skin pigment melanin are called albinos. Normal skin pigmentation is dominant. Use N to represent the allele for normal skin pigment and n to represent the allele for albinism. If you cannot determine the genotype of the dominant phenotype Normal Skin Pigment (genotypes NN and Nn) then write it as N_. Refer to the Figure below and identify the genotype of each individual. Write the genotypes of each individual on the diagram.

How many individuals had the genotype Nn ? _____ How many were N_? _____

Using the Punnett square below predict the probability of the grandparents having albino children.


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14. The following pedigree demonstrates the ability to taste PTC paper. The ability to taste is due to a dominant allele and is represented by the letter T and the non-taster allele is recessive and represented by t. Refer to Figure below and identify the genotypes as you did in the previous pedigree.

How many individuals are heterozygous? _____ How many are homozygous ? _____

What is the probability of I3 and I4 having non-taster offspring ? _____ (Hint: Use the Punnett square below)


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15.

Is the allele for the condition autosomal dominant or recessive? ______________________

Identify the genotype for each individual using the above table. Use A_ if undetermined. 16.

Is the allele for the condition autosomal dominant or recessive? ______________________ Identify the genotype for each individual using the above table. Use A_ if undetermined.


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17. The Blue People Of Troublesome Creek Six generations after a French orphan named Martin Fugate settled on the banks of eastern Kentucky's Troublesome Creek with his redheaded American bride, his great-great-great-great grandson was born in a modern hospital not far from where the creek still runs. The boy inherited his father's lankiness and his mother's slightly nasal way of speaking. What he got from Martin Fugate was dark blue skin. "It was almost purple," his father recalls. Doctors were so astonished by the colour of Benjy Stacy's skin that they raced him by ambulance from the maternity ward in the hospital near Hazard to a medical clinic in Lexington. Two days of tests produced no explanation for skin the colour of a bruised plum. A transfusion was being prepared when Benjy's grandmother spoke up. "Have you ever heard of the blue Fugates of Troublesome Creek?" she asked the doctors. "My grandmother Luna on my dad's side was a blue Fugate. It was real bad in her," Alva Stacy, the boy's father, explained. The doctors finally came to the conclusion that Benjy's colour was due to blood inherited from generations back. Benjy lost his blue tint within a few weeks, and now he is about as normal looking a seven-year-old boy as you could hope to find. His lips and fingernails still turn a shade of purple-blue when he gets cold or angry, a quirk that so intrigued medical students after Benjy's birth they would crowd around the baby and try to make him cry. "Benjy was a pretty big item in the hospital," his mother says with a grin. Dark blue lips and fingernails are the only traces of Martin Fugate's legacy left in the boy; that, and the recessive gene that has shaded many of the Fugates and their kin blue for the past 162 years. Given below is a pedigree of some of the blue people of Troublesome Creek


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17. continued

The trait is called Methemoglobinemia and is inherited as an autosomal recessive allele, which

means that affected individuals have _______ copies of a mutant allele.

Indicate which individuals are carriers of the “blue” gene by placing the letters Bb next to their symbol.

What is the relationship of the parents of the “blue” children?

What is the probability that the unaffected siblings of the “blue” children are carriers for the “blue” trait?

What warning does marrying close relatives does this illustrate?


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18. Haemophilia: The X chromosome also carries genes that help control blood clotting. A recessive allele in either of these two genes may produce haemophilia. In haemophilia, a protein necessary for normal blood clotting is missing. Haemophiliacs can bleed to death from cuts and may suffer internal bleeding if bruised.

If a woman who has normal blood-clotting but is a carrier for haemophilia marries a man who is a haemophiliac, what are the chances their daughters will be haemophiliacs like their father? Use The Eight Steps to answer the question


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19. Colourblindness: Three human genes associated with colour vision are located on the X chromosome. In males, a defective version of any of these genes produces colourblindness. Red/Green colourblindness is a sex-linked trait. If a man with normal colour vision marries a colourblind woman, will all of the offspring be colorblind? If not, who will not be colourblind (sons or daughters)? Use The Eight Steps to answer the question


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Appendix The Eight Steps

1. Set up Genetic Hypothesis Number of genes Number of alleles per gene Which allele is dominant and which allele is recessive (or co-dominant) e.g. 1 gene, 2 alleles, red allele is dominant to white allele

2. Assign Allele symbols

e.g. R = Dominant red colour allele r = recessive white colour allele IA = co-dominant A allele IB = co-dominant B allele

3. Show P (parental) phenotypes e.g. Red coloured flowers × Red coloured flowers

4. Show P genotypes

e.g. Rr × Rr

5. Show P ova/sperm Punnett square

6. Show offsprings’ genotypes and frequencies

e.g. ¼RR : ½Rr : ¼rr

7. Show offsprings’ phenotypes and percentages e.g. 75% red coloured flowers and

25% white coloured flowers

8. Answer the question e.g. There will be 75% red coloured flowers and 25% white coloured flowers

R r

R RR Rr

r Rr rr


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Notes, Clues and Hints for Pedigrees In pedigrees, the symbol for female is a circle (think of a pregnant woman ‘round’ in shape). Autosomal Recessive Traits • Equal numbers of affected males and females (black solid symbol) • Affected individuals (aa) usually appear every second generation (i.e. the disorder

jumps a generation) • Affected individuals usually have unaffected parents (heterozygous Aa carriers)

Autosomal Dominant Traits • Equal number of affected males and females (BB or Bb) • Affected individuals (B_) usually appear every generation • Affected individuals have at least one affected parent who is heterozygous (Bb)

Sex-Linked Recessive Traits (gene locus is on the X chromosome) • Predominantly males affected (XdY) • Affected females (XdXd) usually have an affected father (XdY) and an unaffected (carrier)

mother (XDXd) • Affected individuals usually appear every second generation • Affected males usually have unaffected parents (mother is carrier [XDXd] and father is

normal [XDY])

Sex-Linked Dominant Traits (gene locus is on the X chromosome) • Slightly more females affected (XEXe) than males (XEY) • Families with affected fathers (XEY) and unaffected mothers (XeXe) only have affected

daughters (XEXe) and unaffected sons (XeY) • Families with unaffected fathers (XeY) and affected mothers (usually XEXe) can have

affected (XEXe) and unaffected (XeXe) daughters plus affected (XEY) and unaffected (XeY) sons

• Affected individuals usually appear every generation

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